Rachel Wald always has a bit of a cold. That’s life when you have two kids younger than 5, she says. You’re always a little sick. But it wasn’t until after Wald and her family voluntarily fled the fires in Los Angeles that she realized the cough, sore throat, and itchy eyes she couldn’t shake were caused by the fires plaguing the city. “I don’t think I was really recognizing how much of it was not the cold, but the smoke,” she said.
Wald, who is a director at a health and environment center at the University of Southern California, is among the lucky ones. Her neighborhood in central L.A. was never directly threatened. Her house is intact; her children, husband, and all they own are safe. Nevertheless, Wald, like millions of other Angelenos, can’t escape the health effects of the blazes. Experts expect those impacts to linger.
The wind-driven fires that have leveled a broad swath of Los Angeles have killed at least 25 people, consumed approximately 12,000 homes, schools, and other structures, and burned more than 40,000 acres since January 7. In the aftermath of such disasters, the focus is rightfully on treating the injured, mourning the dead, and beginning the long process of recovery. In time, though, attention shifts to the health consequences that reverberate days, weeks, even years after the danger has passed.
Wildfires, a natural part of many ecosystems, particularly in the West, typically occur in forests or where wildlands meet communities. It is extraordinarily rare to see them penetrate an American city, but that’s exactly what happened in the nation’s second-largest metropolis.
As state and federal agencies assess the damage, researchers say the health effects of the wildfires must be tallied just as meticulously.
“These fires are different from previous quote-unquote ‘wildfires,’ because there are so many structures that burned,” said Yifang Zhu, a professor of environmental health sciences at the University of California, Los Angeles. “Everything in the households got burned — cars, metal pipes, plastics.”
Wildfire smoke is toxic. Burning trees and shrubs produce very fine particulate matter, known by the shorthand PM 2.5, which burrow deep into the lungs and can even infiltrate the bloodstream, causing cold- and flu-like symptoms in the short term, and heart disease, lung cancer, and other chronic issues over time.
But the fires that raced through Los Angeles burned thousands of homes, schools, historic buildings, and even medical clinics, blanketing the city in thick smoke. For several days after the first fire started, the city’s air quality index, or AQI, exceeded 100, the threshold, typically seen during wildfires, at which air becomes unhealthy to breathe for children, the elderly, and those with asthma. In some parts of the city, the AQI reached 500, a number rarely seen and always hazardous for everyone.
At the moment, air pollution experts know how much smoke fills the air. That’s shown improvement in recent days. But they don’t know what’s in it. “What are the chemical mixtures in this smoke?” asked Kai Chen, an environmental scientist at the Yale School of Public Health. “In addition to fine particulate matter, there are potentially other hazardous and carcinogenic organic compounds — gas pollutants, trace metals, and microplastics.”
Previous research shows that the spikes in unhealthy air quality seen during such events lead to higher rates of hospitalizations for issues like asthma, and even contribute to heart attacks among those with that chronic disease. A 2024 study on the long-term effects of smoke exposure in California showed that particulate matter from wildfires in the state from 2008 to 2018 contributed to anywhere from 52,000 to 56,000 premature deaths. A health assessment of 148 firefighters who worked the Tubbs Fire, which burned more than 36,000 acres in Northern California in 2017 and destroyed an unusually high number of structures, found elevated levels of the PFAS known as forever chemicals, heavy metals, and flame retardants in their blood and urine.
The L.A. County Department of Public Health has formally urged people to stay inside and wear masks to protect themselves from windblown toxic dust and ash. Air quality measurements don’t take these particles into account, which means the air quality index doesn’t reveal the extent of contaminants in the air.
Zhu and her colleagues have been collecting samples of wildfire smoke in neighborhoods near the fires. It’ll be months before that data is fully analyzed, but Zhu suspects she will find a dangerous mix of chemicals, including, potentially, asbestos and lead — materials used in many buildings constructed before the 1970s.
The risk will linger even after the smoke clears. The plumes that wafted over the landscape will deposit chemicals into drinking water supplies and contaminate soil. When rains do come, they’ll wash toxic ash into streams and across the land, said Fernando Rosario-Ortiz, an environmental engineer and interim dean of the University of Colorado Boulder environmental engineering program. “There’s a lot of manmade materials that are now being combusted. The potential is there for contamination,” he said, noting that little research on how toxic ash and other byproducts of wildfires in urban areas currently exists. “What we don’t have a lot of information on is what happens now.”
After the Camp Fire razed Paradise, California, in 2018, water utilities found high levels of volatile organic compounds in drinking water. Similar issues have arisen in places like Boulder County, Colorado, where the Marshall Fire destroyed nearly 1,000 structures in 2021, Rosario-Ortiz said, though the presence of a contaminant in a home doesn’t necessarily mean it will be present in high levels in the water. Still, several municipal water agencies in Los Angeles issued preemptive advisories urging residents not to drink tap water in neighborhoods near the Palisades and Eaton fires. It’ll be weeks before they know exactly what’s in the water.
As wildfires grow ever more intense and encroach upon urban areas, cities and counties must be prepared to monitor the health impacts and respond to them. “This is the first time I’ve ever even witnessed or heard anything like this,” said Zhu, who raised her daughter in Los Angeles and has lived there for decades, said. “Even being in the field studying wildfires and air quality impacts, I never imagined that a whole neighborhood, a whole community in Palisades, would burn down.”
Wald is back home. She’s still got a nasty cough, but her other symptoms are starting to subside as the smoke in her neighborhood clears. The fires gave her a scare, but she’s not making long-term plans to move on just yet. “I wouldn’t say that here where I am right now, I’m that worried,” she said. “But, I mean, it’s not great.”
